Unlike tangible entities such as industrial products or food products, digital contents are easily copied and reproduced in the original states. Although unauthorized or illegal reproduction (copying) of contents is banned under the Copyright Law, there are still many unauthorized or illegal copies being made in reality. Robust protection for the copyrights of contents is a major concern of content creators, and is in serious demand.
In recent years and continuing, digital rights management (DRM), a copyright management technique for digital contents, has been attracting attention. At first, DRM techniques applied to music CDs, DVD videos, or digital broadcasting came to the front, and then, the DRM technique applied to mobile or cellular devices has been attracting much attention along with availability of a variety of types of contents and increase of prices.
In response to the demand, standardization of DRM is being promoted by the Open Mobile Alliance (OMA), which is a standards body for the technology of mobile software application elements. With OMA DRM, arbitrary contents delivered to mobile devices are to be protected by not only restricting reproduction or copying of content under the protection of the Copyright Law, but also allowing designation of limitations (limited number of uses or expiration dates for use). The OMA DRM is furnished with various functions responding to the demands from contents providers, and one of such functions is a super-distribution function enabling distribution of digital contents by separating the copyright-protected contents from their rights information.
There are two versions of OMA DRM, namely, OMA DRM version 1.0 (DRMv1.0, see Non-Patent Document 1 listed below), which is a basic technique for less expensive contents, and OMA DRM version 2.0 (DRMv2.0, see Non-Patent Document 2 listed below), which is an advanced technique targeting expensive contents.
FIG. 1 is a schematic diagram illustrating the super-distribution function realized by the OMA DRM. With OMA DRM, the copyright-protected content 1002 and the rights information (rights object) 1003 are separated from each other, and delivered independently from each other. Super-distribution is a delivering scheme that allows free reproduction or redelivering of the content 1002, but values the rights information 1003. The content 1002 is encrypted, and it cannot be used unless the content key contained in the rights information 1003 is acquired. A new content using scheme, in which the user transmits the encrypted content 1002 to a friend by, for example, e-mail and the friend purchases the rights information 1003 by himself (or herself), can be established.
The encrypted content 1002 is binarized according to the DRM content format (DCF). The DRM content format includes a URL of the rights issuer (RI) who holds the rights information 1003. The mobile device 1001 accesses the URL of the rights issuer to request delivery of the rights information 1003 that contains the content key. This arrangement realizes distribution of digital contents, while protecting the digital copyrights through encryption.
Another known technique is a data management service system for cellular phones (see, for example, Patent Document 1 listed below). In this system, to remove inconvenience when the information and data used in an old cellular phone become unavailable when the old one is replaced with a new one, while maintaining protection of the copyrights of the contents such as software applications, the information and data used in a cellular phone are stored in the data management server provided on a network. The information and data items furnished with author's (creator's) IDs are stored in the copyright protection area, and removal or transfer to another storage area is restricted. The data items stored in the copyright protection area can be downloaded only to the cellular phones associated with the protected data items. Accordingly, the contents can be continuously available for the user even if the cellular phone is replaced with a new one because the information and data items are uploaded to and downloaded from the data management server as necessary.
Still another known system is one that uses a license management server. If content downloaded from the network to a cellular phone is not used for a certain period, the license is sent from the cellular phone to be deposited in the license management server on the network in exchange for a certificate or a token. When the content is used again in the cellular phone, the license is acquired from the license management server based upon the certificate or the token. (See, for example, Patent Document 2 listed below).
Under the digital copyright management of the OMA DRM, unrestricted distribution (including transmission) of contents is permitted, but the rights information is prohibited from being freely distributed (including transmission from a cellular phone). If a cellular phone is lost or broken after its content and the associated rights information are acquired, the same content and the rights information have to be acquired again from the content provider. In addition, payment for acquiring the rights information may have to be made again, depending on the situation.
When replacing a cellular phone with a new model, the cellular phone is connected via a memory transfer device to an information processor to electronically read the private data such as telephone numbers out of the memory and to write the data into the memory of the new cellular phone in the shop. To reproduce the contents under the copyright protection, licenses from the content creators are required. However, since it is not easy to obtain a license from each of the creators, the rights information of the protected contents are not written into the new cellular phone. This means that the user cannot continue to use the purchased contents in the new cellular phone.
The data management service system disclosed in Patent Document 1 is designed such that whether to upload the content created by a content creator to the server is determined by the user. In fact, the user has to obtain a license from the content creator or the author to reproduce the copyright-protected content for uploading to the server. However, this system cannot prevent malicious users from uploading or reproducing unauthorized contents in the server, and consequently, the reproduction right of the author is likely to be infringed.
In addition, this publication does not address the issue focused on the rights information of the contents. Restriction on use of content (e.g., limitation of number of uses or expiration date) may be designated in the rights information of the content. Such restriction information is status information that changes every time the content is used. However, the conventional data management service system only handles the issues occurring in uploading and downloading data and information to and from the server, and it does not deal with the procedure required when the status information has varied along with use of the content. If the cellular phone is lost, the current limitation or restriction information as to the use of the content cannot be taken over to a new cellular phone. For example, if up to five times use is permitted in the rights information, and if the user has reproduced the content three times on the cellular phone, then two more uses are left for the user. However, there is no disclosure about how to deal with the status information representing two more chances to reproduce the content being left. Thus, the status information cannot be correctly taken over when the cellular phone is replaced with a new one.
In the system of Patent Document 2 that supplies a license exchange certificate or token to the cellular phone, the license exchange certificate itself is lost if the cellular phone is lost, and therefore, the license deposited in the server cannot be returned to the cellular phone. This publication does not disclose procedures for reissue or takeover of the license exchange certificate by the new cellular phone. After all, a new license has to be acquired.                [Non-Patent Document 1] Open Mobile Alliance, “OMA Digital Rights Management Enabler Release”, Approved Version 1.0, OMA-DRM-V1—0-20040615-A, June 2004, www.openmobilealliance.org.        [Non-Patent Document 2] Open Mobile Alliance, “OMA Digital Rights Management Enabler Release”, Approved Version 1.0, OMA-DRM-V2—0-20040715-C, July 2004, www.openmobilealliance.org.        [Patent Document 1] JP (Kokai) 2004-200845 A        [Patent Document 2] JP (Kokai) 2003-179590 A        